in every collision there will be always an impulse I which represents change in momentum and is always constant. Thus, I = F x t = constant. Hence whenever, there is a change in impact ie force, there will also be equal change in time or vice versa. Thus, increae of time will decrease impact ie., force.
e.g., a person gets less injured on sand floor when compared to cemented floor when jumping from same height due to increase of time and decrease of force.